Copolymerization of Caprolactone Isomers to Obtain Nanoparticles with Constant Hydrophobicity and Tunable Crystallinity

To obtain a set of polycaprolactones (PCL) with varying crystallinity, the triazabicyclodecene-catalyzed copolymerization of the two constitutional isomers ε-caprolactone (εCL) and δ-caprolactone (δCL) was carried out at room temperature in toluene. Variation of the feed fraction of εCL from 50% to 80% and the detailed kinetic studies accompanied by application of terminal as well as nonterminal kinetic models suggested the formation of random copolymers. Differential scanning calorimetry and wide-angle X-ray scattering investigations revealed the decrease of melting temperatures and degree of crystallinity with the εCL fraction in the PCL. All copolymers were suited to obtain aqueous nanoparticle dispersions by means of nanoprecipitation. Encapsulation of the fluorescent probe pyrene confirmed a constant hydrophilic/hydrophobic balance of the nanoparticles.